1. Field of the Invention
The present invention relates to a coal upgrade plant which pyrolyzes coal after drying the coal, and a method for manufacturing upgraded coal.
2. Description of Related Art
Since low ranking coal such as sub-bituminous coal and lignite has a lower carbonization degree and a higher water content than high ranking coal, a calorific value per unit weight is lower. However, since there are abundant deposits of low ranking coal, the low ranking coal is desired to be effectively used. Thus, various coal upgrading techniques have been studied in which the calorific value of the low ranking coal is increased by performing pyrolysis after drying the low ranking coal, and upgraded coal is deactivated so as to prevent spontaneous combustion during transportation or storage (e.g., Japanese Unexamined Patent Application, Publication No. 2014-31462 (hereinafter referred to as JPA 2014-31462)).
JPA 2014-31462 discloses that pulverized coal is fed into a pyrolysis furnace, and mercury-based substances (HgS, HgCl2 or the like) contained in a pyrolysis gas generated when coal is pyrolyzed are adsorbed to the pulverized coal and discharged outside of a system in order to prevent an increase in the concentration of mercury in pyrolyzed coal with the mercury-based substances being re-adsorbed to the pyrolyzed coal.
A temperature of pyrolyzing coal is 300° C. or more to 500° C. or less, and an evaporating temperature of mercury is about 400° C. Thus, it can be said that it is technically appropriate to take into consideration the generation of the mercury-based substances in a pyrolyzer as described in JPA 2014-31462. Under such understanding, since a dryer used before the pyrolysis heats the coal to 150° C. or more to 200° C. or less to remove moisture in the coal, it has been considered that the generation of the mercury and/or the mercury-based substances is small enough to be negligible.
However, as a result of earnest study, the present inventors confirmed that there is a possibility that a non-negligible amount of mercury and/or mercury-based substances is generated in the dryer used for removing the moisture in the coal.
The present invention has been made in view of such circumstances, and an object thereof is to provide a coal upgrade plant and a method for manufacturing upgraded coal capable of removing mercury and/or mercury-based substances generated in a dryer.